{Dangerous Content?} Obfuscation Toolkit Question....

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I am using DBMS_OBFUSCATION_TOOLKIT to encrypt certain sensitive columns.

I also have a need to compare those columns and hence the need to store the same values in a hash value so that it can be compared when sent to clients with the hash value key. The encrypted values by the OBFUSCATION_TOOLKIT cannot be compared from what I know. How do generate hash values for the data already stored in the database and use the same for comparing etc ? Has anyone worked on this ? ANy function written that I can use ? I need this first for a demo(urgent) and then for the actual implementation (breather of two weeks). Any help , pointers will be appreciated.